Microelectromechanical systems (“MEMS,” also referred to as “MEMS devices”) are a specific type of integrated circuit used in a growing number of applications. For example, gyroscopes and accelerometers can be formed as MEMS devices. In simplified terms, such MEMS devices typically have one or more movable structures suspended above a substrate, and associated circuitry (on chip or off chip) that both senses movement of the suspended structure(s) and delivers the sensed movement data to one or more external devices (e.g., an external computer). The external device processes the sensed data to calculate the property being measured (e.g., rotational or linear motion).
Distortion of the geometry of a MEMS device having an oscillating mass, such as a gyroscope, can produce an imbalance in the forces transverse to a longitudinal drive finger. This imbalance can cause a net force that is indistinguishable from a Coriolis force. Consequently, a gyroscope can produce false outputs. There are at least two sources of these geometric distortions. One arises from surface shear of the substrate (e.g., from release/wafer curvature on dicing). Another arises from differential expansion of the package and applied accelerations (e.g., diagonally, G×G).